1. Field of the Invention
The present invention relates to the isomerization of haloalkenes, and more particularly, but not by way of limitation, to the isomerization of trans-1,4-dichlorobutene-2 to 3,4 dichlorobutene-1.
2. Description of the Prior Art
A number of catalytic systems have been proposed for accomplishing the isomerization of a- dichlorobutene such as trans-1,4-dichlorobutene-2. The general object of these systems has been to obtain the desired dichlorobutene in high yield at a relatively low temperature, thereby reducing the decomposition of dichlorobutene and the production of high-boiling tar by-products. A further object of these prior art systems has been to reduce the amount of catalyst necessary to effect the isomerization. Accordingly, the prior art systems have sought to produce high catalytic activity at a low concentration of catalyst.
The prior art discloses the combination of at least one of the metal salts of copper, iron, zinc and aluminum and of an auxiliary catalyst in the presence of a heated dichlorobutene to accomplish an isomerization of the dichlorobutene. For instance, U.S. Pat. No. 4,328,381 to Tabata et al. discloses a combination of a copper compound and a dithiocarbamic acid derivative containing a tertiary amine, with the copper compound being present in a concentration in the range of 0.005 to 1 weight percent and the dithiocarbamic acid derivative being present in a concentration of 0.01 to 2 weight percent. The reaction temperature is suggested as in a range of 80.degree. to 150.degree. C. A different system is disclosed in British Patent No. 798,889, wherein an organic amine is combined with a copper salt.
As shown by these disclosures, there is a need for a catalyst system that is effective in promoting the isomerization of haloalkenes such as trans-1,4-dichlorobutene-2 at low temperatures and at low catalyst concentrations, whereby the decomposition of the haloalkenes, the production of high-boiling by-products, and corrosion of those parts of the apparatus coming into contact with the catalyst solution are minimized.